C1256 code

Hi, suddenly while driving car the dash board showed all brake lights (ABS, parking, anti slip) and brake became weak and after press at pedal sound come from left side to engine even when press while car is not turned on as buzzing sound, when start it the sound come and go in regular pattern. I plugged obd and showed the above code which mean there is low pressure actuator.
What is the problem? Does it need replace the actuator which cost too much or may be simple thing like sensor?
I hope you can tell me what parts that may be fault. And how to deal with this problem.
Thanks